Method for producing naphthalene

ABSTRACT

HYDROCARBON MIXTURES, SUCH AS LIGHT CYCLE OILS FROM A CATALYTIC CRACKING UNIT, ARE SELECTIVELY SEPARATED BY A CYCLIC ADSORPTION TECHNIQUE INVOLVING PASSING THE HYDROCARBON MIXTURE THROUGH A FIXED BED OF ACTIVATED CARBON TO ADSORB SELECTIVELY POLYCYCLIC AROMATIC COMPONENTS AS AN ADSORBATE PHASE WHILE COLLECTING LESS READILY ADSORBED COMPONENTS AS A RAFFINATE PHASE; PASSING A FIRST PORTION OF A PREDETERMINED VOLUME OF CARBON DISLFIDE THROUGH THE CARBON TO DISPLACE THE ADSORBATE PHASE WHILE COLLECTING A PORTION OF THE RAFFINATE PHASE AS A RECYCLE STREAM; PASSING THE REMAINDER OF THE CARBON DISULFIDE THROUGH THE CARBON WHILE COLLECTING AN ADSORBATE PHASE; PASSING A FIRST PORTION OF THE COLLECTED RECYCLE MATERIAL, THROUGH THE CARBON WHILE COLLECTING AN ABSORBATE PHASE; PASSING THE RE-   MAINDER OF THE COLLECTED RECYCLE MATERIAL THROUGH THE CARBON WHILE COLLECTING A RAFFINATE PHASE; SEPARATING CARBON DISULFIDE FROM THE RAFFINATE AND ADSORBATE PHASE FOR REUSE AS A DISPLACING FLUID; PASSING THE ADSORBATE TO AT LEAST ONE HYDROGEN TREATING OPERATION UNDER CONDITIONS SUCH THAT RESIDUAL ALIPHATIC HYDROCARBONS ARE CRACKED, RESIDUAL ALKYL MONOCYCLIX HYDROCARBONS ARE DEALKYLATED, POLYCYCLIC AROMATICS REMAIN UNREACTED AND THE MIXTURE IS DESULFURIZED, SEPARATING THE HYDROGEN-TREATED PRODUCT INTO A LIGHT FRACTION AND A HEAVY FRACTION AND SUBJECTING THE HEAVY FRACTION TO A HYDRODEALKYLATION TREATMENT TO PRODUCE SUBSTANTIAL VOLUMES OF NAPHTHALENE.

Oct. 10, 1972 ARPENTER ETAL 3,697,414,

METHOD FOR PRODUCING NAPHTHALENE Filed April 1971 2 Shoots-Sheet 2 m 0 3 0 1 2 E 4 Y in 'g g z N 2 U U 2 LI 0 F q) I CD a U) a 8 z I O- LIJ r O Y 8 S INVENTORS XBCINI 3A|DvaJ3a DAVID B. CARPENTER EDWARD A- THONPSON BY -%A%az ATTORNEY United States Patent Office Patented Oct. 10, 1972 3,697,414 METHOD FOR PRODUCING NAPHTHALENE David B. Carpenter, Hackettstown, N.J., and Edward ABSTRACT OF THE DISCLOSURE Hydrocarbon mixtures, such as light cycle oils from a catalytic cracking unit, are selectively separated by a cyclic adsorption technique involving passing the hydrocarbon mixture through a fixed bed of activated carbon to adsorb selectively polycyclic aromatic components as an adsorbate phase while collecting less readily adsorbed components as a raflinate phase; passing a first portion of a predetermined volume of carbon disulfide through the carbon to displace the adsorbate phase while collecting a portion of the raflinate phase as a recycle stream; passing the remainder of the carbon disulfide through the carbon while collecting an adsorbate phase; passing a first portion of the collected recycle material through the carbon while collecting an adsorbate phase; passing the remainder of the collected recycle material through the carbon while collecting a rafiinate phase; separating carbon disulfide from the raffinate and adsorbate phase for reuse as a displacing fluid; passing the adsorbate to at least one hydrogen treating operation under conditions such that residual aliphatic hydrocarbons are cracked, residual alkyl monocyclic hydrocarbons are dealkylated, polycyclic aromatics remain unreacted and the mixture is desulfurized, separating the hydrogen-treated product into a light fraction and a heavy fraction and subjecting the heavy fraction to a hydrodealkylation treatment to produce substantial volumes of naphthalene.

BACKGROUND OF THE INVENTION Field of the invention The present invention relates to the production of naphthalene from a light cycle oil of a catalytic cracking operation by contacting the cycle oil with activated carbon to selectively adsorb the polycyclic aromatics; thereafter displacing the polycyclic aromatics with carbon disulfide; and subjecting the desorbed polycyclic aromatics to hydrodealkylation.

Description of the prior art One of the primary products sought to be recovered in refinery operations because of its commercial value is naphthalene. The chemical importance of naphthalene resides primarily in its use as an intermediate in the production of phthalic anhydride. For example, roughly 80% of all of the naphthalene produced domestically is consumed in the production of phthalic anhydride.

Heretofore, the primarily source of naphthalene has been coal tar fractions. However, the uncertainties and fluctuations in the production of coal tars makes it undesirable to tie the production of naphthalene to such variable sources of coal tars, particularly since the major por- 18 Claims tion of coal tar is produced as a by-product of the manufacture of coke for the productionof steel.

Naphthalene does not exist in any great volumes in crude petroleum hydrocarbons. While the amounts of naphthalene in crude oils varies to some extent, the total of all aromatic hydrocarbons in petroleum is usually only about 5%. Accordingly, it is impractical to separate such naphthalene from the crude by simple distillation, since a number of other contaminating materials boil in the same boiling range. However, certain refined petroleum fractions, such as fractions obtained as products of catalytic reforming, catalytic cracking and thermal cracking, do contain significant quantities of naphthalene and alkylsubstituted naphthalenes to be of interest as feedstocks for further processing. Some feedstocks, and, particularly, products of catalytic cracking, contain large quantities of naphthalenes and alkyl-substituted naphthalenes and only minor quantities of monocyclic aromatics and parafiins. These feeds may, therefore, be directly processed in a hydrodealkylation unit to convert the alkyl naphthalenes to naphthalene. However, when attempting to process fractions containing smaller amounts of naphthalene precursors, it becomes impractical and prohibitively expensive, to directly hydrodealkylate this material since the consumption of hydrogen is extremely high, substantial quantities of valuable hydrocarbons are downgraded to fuel gas, and hydrogen to hydrocarbon mole ratios must be maintained at extremely high levels to prevent excessive reactor temperatures and rapid coke laydown.

While a number of techniques for concentrating naphthalene precursors have been tested in the past, and found useful to a greater or lesser extent, few have been found to economically produce substantial quantities of naphthalene precursors which, in turn, produce economic yields of naphthalene. However, one effective technique has been the utilization of solvents for the separation of paratfins and monocyclic hydrocarbons from dicyclic or polycyclic hydrocarbons in the feed material. While such solvents are effective in varying degrees, the commercial use of such solvents has been practically nil. There are believed to be several basic reasons for such lack of utility and these are primarily directed to the amount of solvent required and hence the cost of operation. In addition, there is a limit to the degree of separation which can be practically and economically effected by the use of a solvent. Even after concentration of polycyclic hydrocarbons by the use of a solvent, there still remain paraffinic and monocyclic aromatic hydrocarbons which boil in substantially the same range as the polycyclic hydrocarbons of interest. Further concentration of polycyclics should also include a reduction of the sulfur content of the hydrocarbon mixture, since hydrocarbon mixtures of the character referred to herein normally contain substantial quantities of sulfur compounds and such sulfur compounds are detrimental to further reactions of the concentrated polycyclic materials.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an improved method for the production of naphthalene. Another object of the present invention is to provide an improved method for the production of naphthalene from petroleum hydrocarbon mixtures. A still further object of the present invention is to provide an improved jecting the dicyclic aromatic adsorbate to catalytic hydrodealkylation. A still further object of the present invention is to provide an improved method for the production of naphthalene wherein a catalytic light cycle oil is subjected to adsorption with an activated carbon, a raffinate phase is collected, adsorbate is displaced with carbon disulfide, the adsorbate phase is separated 'from the displacing fluid, the displacing fluid is recycled to the adsorption step and the adsorbate is subjected to catalytic hydrodealkylation. Another and further object of the present invention is to provide an improved technique for the concentration of polycyclic aromatics from a mixture of polycyclic aromatics, monocyclic aromatics and paraffins; including, separating the polycyclics by adsorption, subjecting the mixture to a hydrogen treatment under conditions to convert the parafiins to lower boiling parafiins, convert the monocyclic aromatics to lower boiling mono cyclic aromatics, and-leave unaltered the polycyclic aromatics; separating the polycyclic aromatics from the remaining materials; and subjecting the polycyclic aromatics to a hydrodealkylation treatment.

These and other objects and advantages of the present invention will be apparent from the following detailed description.

BRIEF DESCRIPTION OF THE INVENTION Briefly, in accordance with thepresent invention, hydrocarbon mixtures are separated by selectively adsorbing polycyclic aromatics on activated carbon; passing carbon disulfide through the activated carbon containing the selectively adsorbed adsorbate to displace the same; recovering thedisplaced adsorbate; and subjecting the adsorbate to a hydrodealkylation treatment to produce substantial volumes of naphthalene.

The present vinvention will be more clearly understood by reference to the drawings when read in conjunction with the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS The details of thepresent invention will be better understood by reference to the drawings, wherein:

FIG. 1 is a flow diagram illustrating the overall method of the present invention; and

FIG. 2 is a plot of refractive index versus time for a single cycle of operation in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION As will be illustrated by the following description, it has been found that the refractive index of the efliuent from the adsorption column of the present invention or a time cycle may be effectively utilized to control the operation of the process of the present invention.

In accordance with FIG. 1 of the drawings, a liquid hydrocarbon feed material is introduced through line and valve 12 to fixed bed adsorption column 14 and thence upwardly through the column. Adsorption column 14 is, of course, filled with a granular activated carbon which will selectively adsorb certain of the components of the feed material. The effluent from column 14, comprising the nowadsorbed components (rafiinate phase), is discharged through line, 16. and valve 18 to accumulator 20. Thereafter, the feed to column 14 is switched from hydrocarbon feed material to carbon disulfide and a predetermined volume of carbon disulfide is passed through column 14.'During the initial start-up of the system, both the point of termination of hyldrocarbon feed and the predetermined volume of carbon disulfide can be determined experimentally by observing a characteristic of the raffiuate phase and/or the adsorbate phase (preferentially adsorbed components), and adjusting the point of termination of the hydrocarbon feed and the volume of carbon disulfide until raffinate and/or adsorbate of the desired character is obtained. For example, the refractive indices of the raffinate and adsorbate phases may be observed, as will be more fully explained hereinafter. Once the point of termination of hydrocarbon feed and the volume of carbon disulfide have been established the system will have reached steady state conditions and'the entire operation can be repeated on the cyclic operating basis hereinafter explained in detail. Sometime after introduction of carbon disulfide is begun, the rafiinate eflluent will contain carbon disulfide. In order to separate the raflinate from the carbon disulfide, the efiluent from accumulator 20 is passed through line 22 to distillation column 24. In distillation column 24 this mixture of rafiinate and carbon disulfide is separated and the rafiinate is discharged through line 26 while the carbon disulfide is discharged through line 26, and thence through line 30 to accumulator 32. Carbon disulfide is fed from accumulator 32 through line 34 and valve 36 to the adsorption column 14. Where necessary, makeup carbon disulfide is introduced to accumulator 32 through line 38 and valve 40. The introduction of carbon disulfide to column 14 is carried out in two distinct phases. During the introduction of a first portion of carbon disulfide, ratfinate discharged through line 26 of distillation column 24 is passed through line 42 and valve 44 to recycle accumulator 46. The amount of rat'- finate collected at this pointcan also be determined by any convenient means. The portions of rafiinate which are not collected in accumulator 46 may constitute the more desirable components of the feed material or the less desirable components of the feed material depending, of course, upon the nature of the feed material. For example, where a light cycle oil is to be separated primarily for the recovery of dicyclic hydrocarbons, the raflinate phase will be the less desirable monocyclic and paraflinic materials. In any event, rafiinate which is not collected may be withdrawn from distillation column 24 through line 48 and valve 50. The raflinate may be stored or otherwise utilized. After the first portion of carbon disulfide has been utilized, the second portion of a predetermined amount of carbon disulfide is passed through adsorption column 14. While the second portion of carbon disulfide is being passed through column 14, an adsorbed or adsorbate phase is passed through line 52 and valve 54 to adsorbate accumulator 56. This adsorbate stream comprises a mixture of the preferentially adsorbed components of the feed mixture and carbon disulfide. The adsorbate passes from accumulator 56 through line 58 to distillation column 60. In distillation column 60, the adsorbate is stripped of carbon disulfide and discharged through line 62 while the carbon disulfide is passed through line 64, and thence through line 30 to accumulator 32. After the predetermined volume of carbon disulfide has been utilized, the recycle raflinate, collected in accumulator 46 is passed through line 70 and valve 72 as a recycle to adsorption column 14. The introduction of recycle to adsorption column 14 is also carried out in two separate phases. As a first portion of the recycle material is passed through adsorption column 14, the efliuent from column 14 constitutes a further portion of the adsorbate phase which is collected and distilled as previously indicated. The end of the first recycle phase is determined in accordance with the previously mentioned criteria for controlling the operation. Thereafter, the second portion of recycle is passed through column 14 until all of the collected recycle has been used. During the introduction of this second portion of the recycle, the efiluent from the adsorption column is switched to the raflinate handling portion of the system and thus is accumulated in accumulator 20 and distilled in distillation column 24. The raflinate is then treated as previously described.

The adsorbate or selectively adsorbed material contains substantial volumes of polycyclic and higher hydrocarbons, whereas the raffinate or non-adsorbed phase is primarily aliphatic and monocyclic hydrocarbons. The adsorbate is then further treated by passing the same through line 74 and valve 76 to accumulator 78. From accumulator 78, the adsorbate passes to line 80 to hydrogen treating unit 82. Hydrogen treating unit 82 is supplied with hydrogen through hydrogen supply line 84, line 86 and valve 88. The product of hydrogen treater 82 is generally passed through line 90 and valve 92 to a second hydrogen treating unit 94. Hydrogen treater 94 is supplied with hydrogen from supply line 84 through line 96 and valve 98. In the preferred operation, hydrogen treater 82 is a hydrodesulfurization unit, whereas hydrogen treater 94 is a hydrocracking-hydrodealkylation unit. The operation of these units and their purposes will be discussed hereinafter in greater detail. In the alternative, hydrogen treater 82 may be operated as a hydrocracker-hydrodealkylator and hydrogen treater 94 may be utilized as a hydrodesulfurization unit. In still another variation, a singel hydrogen treating unitmay be employed, such as unit 82, which would be operated as a hydrocracker-hydrodealkylation unit since an operation of this type does accomplish a certain amount of desulfurization. In this last instance, the product from hydrogen treater 82 would pass through line 100 and valve 2, thereby bypassing the second hydrogen treater 94. Either the product from hydrogen treater 82, passing through line 100, or the product 'of hydrogen treater 94, passing line 104, is then charged to distillation unit 106. In distillation unit 106, the product is separated into an overhead product, which is discharged through line 108 and a bottoms product, which is discharged through line 110. The overhead fraction will generally comprise hydro.- cracked paraflins and dealkylated monocyclic aromatics whose boiling points have been lowered by the hydrocracking-hydrodealkylation treatment and which will then boil below the desired polycyclic materials. In some cases the hydrogen treater may be eliminated. The desired polycyclic material may then be discharged through line 110 to hydrodealkylation unit 112. Hydrodealkylation unit 112 is supplied with hydrogenthrough line 114 and the products. of hydrodealkylation unit 112 are discharged through line 116. The overhead product of line 108 generally is a material boiling in the gasoline boiling range and is a suitable gasoline blending stock. Accordingly,.it

would be passed to gasoline storage or a gasoline treating plant.

A suitable activated carbon for use in accordance with this present invention may have a broad range of particle sizes, for example 4 x 6 to 20 x 50 mesh size (U.S. sieve series). The following physical properties are also desirable:

Total surface area:

(N BET Method mF/g. 500-1500 Apparent density (bulk density, dense packing): I

g./c c. 0.3-0.6 1b./ft. 20-30 Particle density (Hg Displacement), g./cc. 0.5-1.0 Real density (He Displacement), g./cc. 2.0-2.2 Pore volume (within particle), cc./ g 0.5-1.5 Voids in dense packed column, percent 20-50 Specific heat at 100 C. 0.2-0.3

Brunauer, Emmitt and Teller: J. Am. Chem. Soc. 60, 309 (1088),

The following examples illustrate the practice of the present inventionand compare the same with similar techniques.

In all of the examples, the activated carbon utilized as an adsorbent is formed from bituminous coal combined with suitable binders and is activated with steam at a high temperature. The particle size is 12 x 40 mesh size (U.S. sieve series). This activated carbon had the following physical properties.

' TABLE I Physical properties activated carbon Total surface area:

(N BET Method m. /g 1000-1100 Apparent density (Bulk density, dense packing):

Apparent density (bulk density,

dense packing):

g./ CC. 044

- lb./ft. 27.5

Particle density (Hg displacement), g./cc. 0.78 Real density (He displacement), g./cc 2.1 Pore volume (within particle), cc./ g 0.81 Voids in dense packed column, percent 44 Specific heat at C 0.25

(lgqB-pnauer, Emmitt and Teller: .1. Am. Chem. Soc. 60, 309 Except where otherwise noted, the feed material employed was a 430 to 550 F. cut of a light cycle oil from the catalytic cracking operation. Table II below lists the properties of a typical feed material of this type.

TABLE II Properties of light cycle oil Table III below summarizes four cycles of adsorptiondisplacement wherein a light cycle oil heart cut was adsorbed on activated carbon and thereafter displaced by steam stripping at 600 F. It is to be observed that steam stripping is relatively inelfective. The capacity of the carbon decreases very sharply throughout the adsorption-displacement when utilizing steam as a recovery agent. In addition, when polycyclic aromatics are to be separated, the refractive index of the efiiuent rafiinate should be below about 1.5. In the run illustrated, the raffinate refractive index was below that figure for only about 5 to 10 minutes and it rapidly increased to that of the feed material (about 1.5163) after only 18 to 20 minutes. The refractive index of the adsorbate is also too low to be a worthwhile feed material for a hydrodealkylation operation or other operation for the recovery of aromatics since polycyclic concentrates for such use should have a refractive index above about 1.54 and preferably near 1.6. Where the refractive index of a stream, such as rafiinate or adsorbate, is referred to, this represents the 7. refractive index of the particular stream after carbon disulfide. has been removed therefrom.

TABLE Ill-STEAM STRIPPING CARBON A second test was made with the same feed material, the same activated carbon, and in the same equipment but with carbon disulfide as the displacing agent. The results of this test are set forth in Table IV below. It is obvious from Table IV that the capacity of the carbon bed decreased over the first several cycles, but then remained substantially constant. Also, except for the first run when the carbon was dry, the time needed to reach an effluent refractive index of 1.5 after collection of the first efiiuent, was about 10 to 20 minutes. This is more than twice the length of time observed when steam stripping. This shows that the use of carbon disulfide as a displacing media not only provides high carbon capacity but it also gives a higher selectivity'for the naphthalene precursors sought to be extracted from the light cycle oil. Thus, carbon disulfide displacement results in a higher overall carbon capacity and a higher yield of the high refractive index materials. This higher yield of the high refractive index materials is a function of the higher equilibrium capacity of the carbon, the" ability of the carbon disulfide to effectively displace these higher refractive index materials, and the higher selectivity for high refractive index materials which the carbon disulfide imparts to'the carbon.

TABLE IV.-CARBON DISULFIDE DISPLACEMENT Cycle 1 2 3 4 5 6 Charge:

Refractive index. 1. 5160 1.5160 1. 5160 1. 5160 1. 5160 1. 5160 Weight, gms 2, 252 2, 687 2, 651 2, 661 2, 678. 2, 685 Pumped eflnent, gins-.. 896 1, 213 1, 246 1, 286 1, 690 1, 281 Blowdown, 652 706 725 706 304 729 Grams total rafl'mate 1, 548 1, 919 1, 971 1, 992 I, 994: 2, 010 Grams "Adsorbate" 704 768 680 669 684 675 Recovery, gms 641 700 724 664 669 643 Gain or loss, gins -63 ---68 +44 +6 15 --32 Vol. pumped in at 1st efiluent, ccs 1, 435 960 990 870 820 825 Time to 1st efiluent,

min 62 37 40 39 38 35 The quality of adsorbate from the two previous tests is given below.

ADSORBATE QUALITY (Table III Runs) (Table IV Runs) CS2 stripped adsorbate t i e d cl 0 l C 019 I 0 Feed at lsor igtte y i y g y 3 Gas chromatograph:

BMN. 51.0 47.0 40.9 41.7 41.7 BMN- 9.0 9.4 9.2 7.4 7.2 AMN- 4. 7 4. 4.2 4.1 DMN+bipheny1 19.3 23.9 26.9 26.8 27.9 ACE+ 20.1 15.0 19.5 19.9 19.1

Table V below summarizes the results of hydrotreating the adsorbate of the last run and thereafter hydrodealkylating a bottoms product of the hydrotreating.

TABLE V Hydrotreating of adsorbate WHSV 1.0 Temperature, F. 1025 Pressure, p.s.i.g 1000 Hg/HC 7/1 Liquidyield, wt. percent 62.5 Liquid product distillation, vol. percent:

Gasoline 31.2

Hydeal feedstock 68.8

8 Dealkylation of 400 F .+hydrotreated bottoms A series of runs was also made in order to determine whether benzene could be utilized as a desorption medium. While benzene was found to be a fairly effective displacing medium, such displacement required volumetric ratios of benzene to light cycle oil feed of 10 to 1 or greater, in order to recover or more of the light cycle oil hydrocarbons from the adsorbent. This becomes economically prohibitive.

Table VI below summarizes an adsorption displacement run in which recycle of a selected portion of the effluent material was practiced. It is to be noted from Table VI that collection of recycle material was terminated during the cycle when the refractive index of the efiiuent being collected for recycle material reached 1.52.

TABLE VI Fresh feed, gms. 579 Fresh feed, cc 640 Recycle feed, gms. 772 Recycle feed, cc. 8'60 Rafiinate: 1

Weight, gms. 199 Final RI 1.489 Average RI 1.476

Naphthalene precursors, percent 5.2 Yield, wt. percent 36.5

Recycle:

Weight, gms. 807 Volume, cc. 900 Initial R-I 1.489 Final RI 1.520 Average RI 1.512

Adsorbate:

Weight, gms. 349 Average RI 1.550 Naphthalene precursors, percent 51.3 Yield, wt. percent 63.7 Naphthalene precursors recovered, percent on feed 32.7 Cycle time, minutes 255 Adsorption rate, cc./min. 11.5 Desorption rate, cc./min. 23.0 Vol. CS cc. 3,000 No blowdown after adsorption.

Blowdown after desorption.

Table VII shows the results of hydrotreating and thereafter dealkylating the adsorbate obtained from the run of Table VI.

TABLE VIL-DOWNSTREAM PROCESSING OFADSORBATEI adsorbate ultimately Passes through Valves r When the refractive index of the adsorbate reaches a H drotreatln y conditlon s: 0 value of about 1.52, Phase D is terminated and Phase E gfg gj g begins. During Phase E of the operation, recycle is conl y gg e at s.c-f-/bb1-.. 12,000 5 tinued through valve 72 until all of the collected recycle 1.0 Hydmgenmsumpmn,sci/bbl 1,250 efiiuerit 18 used and valves 18 and 50 are open d to di Yield otliquld, weight percent 8?, charge a further portion of raflinate phase. When all f the collected recycle material has been passed through Wt. percent Vol. percent 0 adsorption column 14, Phase E is terminated and the next 5l3 100 100 10 cycle is begun by switching to a Phase A operation. The 0 28.4 31.7 volumes of materials handled during a complete cycle Hydealfeedstock and, of course, the sizing of the equipment utilized in the Dealkylatlon 400 F.+ bottoms:

ilydeal reed wei ht percent 10o operation are, of course, selected so that sufiicient polyggtig fifg ggggg 213 cyclic aromatics are collected in accumulator 42 to con- Yield on LCO,Weightpercent 24.6 tiriuously operate the remainder of the hydrogen treaticomams N 51% ing and hydrodealkylating operations.

I While specific refractive indices are given by way of of condlact of i.; example, the process can be varied depending upon the recyc e P ase an t 6 con uct 0 tests w 1 e Varymg nature of the feed and the desired end product. Efiective other conditions of operation, it was ultimately determined that the Process of the present invention could results can be obtalned by selecting refractive indices as follows: most effectively be carried out by a cycle of operation involving adsorption and displacement in which five End of Phase A distinct phases were practiced. Table VIII below illustrates End Of Phase the general character of this five-phase operation. End of Phase D 145-155 TABLE VIII Phase In Out Valves open Termination of phase A-.-'...-. Feed.. Raffinate plus CS2-.. 12, 18 and 50 When RI of raflinate reaches 1.49.

CS2--. Recycle 36, 18 an 44 When RI of recycle reaches 1.58. G CS1--. Adsorbate plus CS2. 36, E4 and 68 or 76- When all of predetermined volume of CS2 is used. D Recycle ..do 72, 54 and 68 or 76. When RI of adsorbate reaches 1.62. E "do-.-" Rafifinate plus 082.. 72, 18 and 50 When all of collected recycle is used.

In the operation of the adsorption-displacement cycle, Table IXbelow summarizes an optimum treatment of as illustrated in the Table VIII above, the operation is light cycle oil feed when carried out in the five-phase broken down into five phases. It has been found in accyclic manner set forth in Table VIII. cordance with the present invention that switching of the TABLE IX input and output of adsorption column 14 from one phase to the next can be conveniently handled by monitoring Fresh feed, 533 the output stream and performing the switching opera- Fresh feed, cc. 595 tion at such times as certain refractive indices are meas- Recycle feed, 854 ured. It has been found in accordance with the present Recycle feed 950 invention that the refractive index of the effiuent is an R ffi excellent measure of how the adsorption column is oper- Weight, gms, 217 ating and when each phase of the operation is essentially Fi l R1 1.495 completed. The refractive index is, of course, an excellent A .RI 1.475 indicator of the character of hydrocarbons since pure alkyl naphthalenes normally have a refractive index of Rg-cyclez. about 1.6, monocyclic hydrocarbons have lower refrac- Weight 872 tive indices and paratfinic hydrocarbons have still lower q i 980 refractive indices. himal RI 1'495 :Referring now to the above Table VIH, it is to be seen Final RI 1523 that during Phase A of the operation, the light cycle oil Average RI L523 feed is introduced to the system by opening valve 12 and Adsorbate: the non-adsorbed rafiinate is passed through valves 18 Weight, gins. 304 and ultimately 50 for collection or further use. This phase 55 Average RI 1552 of the operation is continued until the refractive index of Naphthalene precursors, percent 56.1 the rafiinate eflluent reaches a value of about'1.49. At this Yield, wt. percent 583 time, valve 36 is opened to introduce carbon disulfide to Naphthalene precursors recovered, percent on adsorption column 14 and Phase B of the operation is eed 32.7 started. During 'Phase B of the o eration, valves 18 nd Cycle time, minutes 150 44 are opened to collect recycle material in accumul t r Adsorption rate, cc./min. 23.0 46. Phase B of the operation continues until the refra Desorption rate, cc./min. 23.0 tive index of the recycle effluent stream bein cens r d CS vol cc. 2000 reaches a value of about 1.58. At this point, Phase C of. N0 blOWdOWII after adsorptionthe opseation begins. Duriing Phase C of the operation, N0 blOWdOWn after desorptionva ve remains open an carbon disulfide' continues to be passed through adsorption column 14. However, valve ggi g s gbg zgg the i (gcdlrecfly dealkylatmg the 54 is opened to discharge adsorbate to adsorbate acrun 0 a e cumulator 56--the rafiinate valve 18 being closed. After a TABLE X predetermined volume of carbon disulfide displacing fluid 7O nealkylation of adsorbate has been utilized, Phase C of the operation is terminated Ad b and Phase D is begun by opening valve 72. to begin the N h l precursors, percent 5 passage of recycle fluid from accumulator 46 through W i l percent 100 adsorption column 14. At the same time, valve 54 re- Naphthalene, percent 43-46 mains open to discharge adsorbate to accumulator 56. The Yield on LCO 25.0-26.8

The first column of Table XI compares operation in accordancewith the present invention when the activated carbon had been used for six cycles of adsorption-displacement with a similar operation as set forth in column two where the carbon had been used for seventy-nine cycles of adsorption-displacement. It is, of course, quite obvious from the data of Table XI that no observable deactivation of the carbon takes place and it is just as efi'ective after the 79th cycle as it was after the 6th cycle.

TABLE XI Fresh feed, gms 867 859 Fresh teed, ccs 940 960 Recycle feed, gms 420 460 Recycle feed, ccs 470 505 Column length, feet- 8 8 iiv iit 173 186 mg gms inal RI 1. 492 1. 494 Average RI 1. 467 1. 471 Recycle:

Weight, gms.-- 426 256 Average EL... 1. 515 1. 515

Blowdown used e g gms Avem 'e RI 1. 53s 1. 531 Naphthalene precursors, percent 43. 45. Yield, wt. percent 79.0 78. 1 Naphthalene precursors, percent on feed.. 34. 0 35. 5 CS: used, ccs 3, 000 3, 000 Cycle time, min i. 3 0 212 Desorption rate, ccs/min 11. 5 22 Adsorption rate, ces./min 11.5 22

The only limitations on the type of material treated in the adsorption column appear to be that there be no suspended solids in the liquid and the operating temperature should notbe over 100 F., since such high temperatures.cause the carbon dissulfide to decompose. Hence, any material which is too viscous to pass through the column at temperatures below 100 F. should not be utilized in the process. However, such materials may be diluted with an appropriate solvent to permit handling in this process. The adsorption operation should not be conducted below 60 F. and preferably not below 75 F. Column pressures of 15 to 35 p.s.i. are suitable.

As a general proposition, flow rates of both feed and displacing fluid may vary anywhere between 0.05 gallon per minute per square foot of cross-section of the carbon column to as high as gallons per minute per square foot. A preferred rate is 2.0 to 4.5 gallons per minute per square foot for feed and displacing fluid. The recycle rate is preferably 3.5 to 5.0. Experimentation has shown that there is no real advantage in utilizing a column greater than about 10 feet in length. However, by dou- =bling the length of the bed, the flow rate can be doubled and plantcapacity increased accordingly. The carbon disulfide-to-feed ratio may also vary considerably. This ratio should be atleast 1 to 1 but may be anywhere above this limit. As the previous data has indicated, it is possible to recover a very pure methyl naphthalene fraction by increasing the amount of carbon disulfide employed. However, this increases the expense of removing carbon disulfide from the product. The use of such high carbon disulfide ratios also require increased capital investment due to the, fact that the carbon disulfide is toxic and explosive.

The first hydrogen treating operation may be carried out under conventional conditions and utilizing conventional hydrodesulfurization catalysts. For example, the temperature may be between about 400 and 1000 F., at a pressure of about 50 to 2000 p.s.i.g., and a liquid hourly space velocity between about 0.1 and 20, and hydrogen rate between about 500 and 15,000 standard cubic feet per barrel of feed may be employed. Also, a wide variety of catalysts may be utilized. Preferably, any hydrogenation metal on an inert oxide carrier may be utilized. For example, platinum, nickel, cobalt, molybdenum, tungsten, and mixtures of these materials on alumina, silica, or silica-alumina carriers may be utilized. The hydrocracking-hydrodealkylation catalysts hereinafter mentioned may also be utilized in the hydrodesulfurization step under hydrodesulfurization conditions.

The second hydrogen treating operation is carried out in the presence of a cracking catalyst. Catalysts of this nature containing a Group VIII metal alone or in combination with other metals have been found most outstanding. It has been found that under the conditions set forth herein and when utilizing nickelor cobalt-containing catalysts, excellent results can be obtained in the concentration of polycyclic aromatics from mixtures containing such polycyclic aromatics, paraffins, and monocyclic aromatics boiling in essentially the same boiling range.

The nickel content of the catalyst may vary between about 1 and 60% by weight of the total catalyst, and the nickel may be combined with other metals. By far the most effective catalyst in accordance with the present invention is one containing about 3% nickel and about 3 to 15% molybdenum, deposited on an alumina carrier. The combinations of nickel, molybdenum and cobalt on activated alumina have also been found effective. Catalysts containing 4% nickel, and 16% tungsten on alumina, 58% nickel on kieselguhr, and a coprecipitate of 60% nickel, as nickel oxide, and alumina have also been found useful. However, none of the latter appear the equal of the first mentioned nickel-molybdenum catalyst. Cobalt, in essentially the same concentrations, can be substituted for nickel in the catalyst system. A particularly effective catalyst for the present purpose is a catalyst containing about 3.5% cobalt oxide and 12.5% molybdenum oxide deposited on an alumina carrier. A similar catalyst can also be formed by depositing the cobalt and molydenum on a silica-alumina base having a ratio of silica/ alumina of 3/1.

The operating conditions of the second hydrogen treating operation are also important to the polycyclic aromatic concentration. Specifically, the temperature should be between about 800 and 1200 F. and, preferably between about 850 and 1050 F. A pressure between about 250 and 5000 p.s.i.g., and preferably above 1000 p.s.i.g., is preferred. The space velocity should be between about 0.2 and 5, and, preferably between about 0.5 and 2. Finally, the hydrogen rate should be between about 2000 and 20,000 standard cubic feet per barrel of feed, and, preferably between 2,000 and 15,000 standard cubic feet per barrel.

The hydrodealkylation unit may be operated under conventional hydrodealkylation conditions and utilizing conventional hydrodealkylation catalysts. A highly effective catalyst for this purpose is chromium on'alumina. Suitable operating conditions include a temperature between 900 and 1400 F., and a pressure between and 1000 p.s.i.g. However, for bestresults, in the converr sion of alkyl polycyclic aromatics to naphthalene, the temperature should be 1200 F. at the entrance to the dealkylation unit and 1350", F. at the exit. The pressure should preferably be between about and 750 p.s.i.g. As previously indicated, the second hydrogen treating operation selectively cracks paraffins and removes (dealkylates) and cracks side chains from mononuclear aromatics without affecting the aromatic ring. In conventional hydrocracking operations, aromatics are partially or completely hydrogenated to naphthenes and the partially saturated aromatics and naphthenes are then cracked to break the ring. In the present invention, the catalyst and conditions are selected so that this normal production of naphthenes and ring destruction is avoided.

13 Once a cycle of operation has been ,set up based on the refractive index cut-point or some other measure of product quality, time cycle control can be utilized to repeat the operation and predictably produce a product 14 1 Table XIV illustrates the effectiveness of time-cycle control in producing polycyclic products from a light cycle oil. It is obvious that by altering the time cycle, products containing anywhere from 50% to 88% naphwhich meets the original specifications. Such time-cycle control has been utilized to produce a high-quality, polythenfiacenaphthene can be Ieadlly Produced and of cyclic hydrocarbon material from the previously discussed greater significance is the, fact that a given product can light cycle 0115. This desirable desorbate was produced be repeatedly produced from the Same feed, utilizing at a nominal 4 gallons per minute per sq. foot feed rate the same time 0 C16 and by initially utilizing a 1.58 refractive index cut-point y f the second phase f the recycle stream w Opera- It is obvious from Table XIV that the first portion of ing in this manner, the desorbate product has a refracthe recycle can be introduced in anywhere from 1450 to of Q g f g to i Polycyghc g g i gfi 1600, the second portion of recycle from 100 to 500 an'a oyie o esoraeisprouce. a e illustrates runs made in this fashion. seconds, fresh feed from 500 to 900 seconds, the first TABLE XII Recycle feed, wt. lbs 123 104. 5 104. 5 102. 5 100 Fresh feed, wt. lbs-.. 4 12. 5 15 17. 5 16.5 Total feed, wt. lbs 127 117 119. 5 120 116 Total cycle time, seconds. 5, 350 5, 200 5, 200 5, 150 5, 300 Raifinete, wt. lbs 15. 7 8.7 9. a 10. 6 9.1

Yield, percent- 82.6 67. 4 68. 4 71. 6 65. 5

Out point 1.5070 1.4950 1.5070 1.4980

Ratfinate RI 1.4830 1.4865 1.4770 1.4780 1.4750

0st in raff., percent- 75.1 32.1 82.1 81.2 82.2

Time, secon 1, 200 $1, 050 1, 000 1, 050 1, 050 Recycle, wt. lbs. 106. 5 108 5. 5 108. 5 99. 5

Cut point RI 1. 5840 1.5825 1.5800 1. 5760 1.5710

Recycle BL--- 1.5275 1.524 1.5250 .5215 1.5250

Time, seconds 2, 300 2, 300 2, 300 2, 300 2, 300 CS: Wash period, seconds. 400 400 400 400 500 Desorbate, wt. lbs 3.3 4. 2 4.3 4. 2 4.8

Yield, percent- 17.4 32.6 31.6 28.4 34.5

Desorbate RI 1.5960 1.5930 1.5940 1.5900 1.5860

Naph.-Ace, percent 88.02 86. 37 86.35 85.7 79. 2

CS2, wt. percent/desorbate 96. 6 96. 1 96 96 95. 5

1 Valve trouble.

Ta l XIII mpa adsorption products having 80% portion of carbon disulfide from 2000 to 2300 seconds, q i t l f'l i d li g and the second portion of carbon disulfide from 500 to t 6 cyc e 01 ee 1 e m ese runs 1200 seconds, and the total cyclic operation may vary from TABLE Kill-CHARACTERIZATION 0F FEEDSTOCKS 5250 to 5800 seconds. This particular time cycle is for a Feed column having a height of 22 feet and a nominal diameter P110, 80% 88% of 4 inches, or 0.088 square feet in cross section and utilizplflnt Hydeal Hydeal ing a 4-gallon per minute per square foot feed rate. Gravity. 21 11.1 9.4 Obviously, for other size columns, the time cycle will i gg 435 456 differ. However, the important point is that once a time :22 g3 g2 cycle has been established by utilizing product quality 459 468 473 as a measure, whether this be by refractive index meas- 22; g2 g3 urements or some other means, the time cycle can then $3 23% g: be utilized to carry out the operation and repeatedly progg g; g? duce products meeting the initial specifications. The cycle 484 490 494 would, of course, change if a radical change in the com- :33 gag g3: position of the feed occurred. However, under normal 62 2 9 10 4 4 operating condtions, this will not be the case and the 2412 s21 95 88. '14 time cycle would normally be reset if a change in feed 13.6 7.95 I 7.46

was made.

TABLE XIV.TIME CYCLE AND YIELDS FOR VARIOUS HYDEAL FEED STOCKS 7 Typical Typical Typical Typical 50% Naph.-Ace. 60% Naph.-Ace. Naph.-Ace. 88% Naph.-Ace.

Feed Efiiuent Time Total Time Total Time Total Time Total Desorbate-.- 1 600 1,600 1 500 1 500 1,450 l 450 1,450 1 450 l)? Raflinate. 1, 700 400 1: 900 550 21000 500 1: 950 Fresh Feed Raflmate- 900 2, 600 800 2, 700 500 2, 500 500 2, 450 CS; Recycle--- 2, 000 4, 600 2, 100 4, 800 2, 300 4, 800 2, 300 4, 750 CS-l Desorbate.-. 1, 200 5, 800 1, 000 5, 800 500 5, 300 500 5, 250 Pounds of desorbate. 16 11. 5 g. Pounds of Naph.-Ace 8. 2 6. 8 12.6 1.2 9 Carbon efiectiveness: Pounds carbon required per 5. 8 7. 1

pound of Hydeal teed.

15 Table shows a comparison of a polycyclic product produced from light cycle oil in accordance with the present invention. as compared with three commercially available materials which are sold for the production of naphthalene from polycyclic hydrocarbon concentrates.

TABLE XV Commercial Present Constituents process A B C Naphthalene 0. 52 9. 1 13. 8 3. 7 Naphthalene 0. 95 l 26. 9 17. 8 13.6 fi-methyltetralln 6. 3 7. 3. 0 N aph.-Ace 92. 49 49. 90 55. 00 74. 10 Acenaphthene 0. 92 4. 2 5. 8 4. 3 Unidentified 5. 12 8. 6 0.3 1. 3

Finally, Table XVI illustrates the results obtained by processing various desorbates produced in the present manner without hydrotreating the adsorbate. The 55% naphthene-acenaphthene desorbate is presented for comparative purposes.

TABLE XVL-DEALKYLATION OF DESORBATE We claim:

1. A method for producing naphthalene from a hydrocarbon mixture containing polycyclic aromatic hydrocarbons, monocyclic aromatic. hydrocarbons and aliphatic hydrocarbons; comprising, contacting said hydrocarbon mixture with activated carbon to selectively adsorb on said carbon said polycyclic aromatic hydrocarbons and leave unadsorbed said monocyclic aromatic hydrocarbons and said aliphatic hydrocarbons; removing said adsorbed polycyclic aromatic hydrocarbons from said carbon by passing carbon disulfide into said carbon; and subjecting said removed polycyclic aromatic hydrocarbons to hydrodealkylation.

2. A method in accordance with claim 1 wherein the hydrocarbon mixture is a light cycle oil obtained from a catalytic cracking operation.

3. A method in accordance with claim 1 wherein the removed polycyclic aromatic hydrocarbons are subjected to at least one hydrogen treatment under conditions to dealkylate residual monocyclic aromatic hydrocarbons and crack residual. aliphatic hydrocarbons.

4. A method in accordance with claim 3 wherein the product of the hydrogen treatment is separated into a low boiling fraction and a high boiling fraction and said high boiling fraction is subjected to the hydrodealkylation treatment.

5. A method in accordance with claim 3 wherein a second hydrogen treatment is carried out under conditions tov desulfurize the product of the first hydrogen treatment.

6. A method in accordance with claim 5 wherein the product of the second hydrogen treatment is separated into a low boiling fraction and a high boiling fraction and said high boiling fraction is subjected to the hydrodealkylation 1 6 selected portion of the effluent from the adsorption-displacement operation is recycled to the adsorption column. 8. A method in accordance with claim 1 wherein a predetermined volume of carbon disulfide is utilized as a displacing fluid.

9. A method in accordance with claim 1 wherein the adsorption displacement is carried out utilizing a multiphase, cyclic operation of a fixed bed of carbon. 1

10. A method in accordance with claim 9 wherein the cyclic operation is controlled by observing'the refractive index of at least one predetermined stream and adjusting the operation as needed.

11... A method in accordance with claim 9 wherein the cyclic operation comprises passing the hydrocarbon mix: ture through the carbon and discharging an efliuent comprising raflinate and carbon disulfide; passing a first portion of carbon disulfide through said carbon and collecting an efiluent comprising a recycle mixture; passing a second portion of carbon disulfied through said carbon and collecting an efliuent comprisingadsorbateand carbon disulfide; passing a first portion of said recycle mixture through said carbon while continuing to collect an efiluent comprising adsorbate and carbon disulfide; passing the remaining portion of said recycle mixture through said carbon and collecting an additional portion of efliuent comprising raflinate and carbon disulfide.

12. A method in accordance with claim 11 wherein the hydrocarbon mixture'is passed through the bed of carbon until the raflinate has a first, predetermined refractive index.

13. A method in accordance with claim 11 wherein the first portion of carbon disulfide is passed through the carbon until the recycle has a second, predetermined refractive index higher than the first refractive index.

14. A method in accordance with claim 11 wherein collection of adsorbate-car-bon disulfide is discontinued when all of a predetermined volume of carbon disulfide has been utilized.

15. A method in accordance with claim 11 wherein collection of the adsorbate-carbon disulfide mixture is discontinued when said adsorbate reaches a third predetermined refractive index lower than the second refractive index. 1

16. A method in accordance with claim 11 wherein the collection of the additional portion of rafiinate-carbon disulfide mixture is discontinued when all of the collected recycle mixture has been used.

17. A method in accordance with claim 9 wherein the cyclic operation is controlled by utilizing a predetermined timeof operation for each phase.

18. A method in accordance with claim '17 wherein the predetermined times are established by observing the refractive index of at least one predetermined stream while simultaneously measuring the time of operation for each phase and selecting the times at which the refractive index is a predetermined value.

References Cited UNITED STATES PATENTS 2,395,491 2/ 1946 Mavity 2 674 SA 2,628,933 2/ 1953 Eagle et al 260-674 SA 2,754,254 7/1956 Hastings et al. 260- 674 SA 2,756,197 7/ 1956 Thorpe et al 260--674 SA 2,848,379 8/1958 Rehner et al 260-674 SA 3,340,316 9/1967 Wackher et al. 260--674 SA .HE'RBERT LEVINE, Primary Examiner U.S. C1."X.R. 260-66 6 SA, 674 SA, 674 N; 208-310 

